CFC radiant heater

ABSTRACT

An IR radiant heater has at least one planar carbon heating element ( 1 ) arranged in a housing, which is transparent or at least partially transparent to IR radiation. At least one carbon heating element ( 1 ) is a carbon fiber-reinforced carbon (CFC) web arranged in a plane and arranged between two plates ( 2, 3 ), of which at least one is transparent or partially transparent.

BACKGROUND OF THE INVENTION

The present invention relates to an IR radiant heater having at leastone two-dimensional (planar) carbon filament in a housing that istransparent or at least partially transparent to IR radiation.

Such an IR radiator is realized according to European published patentapplication No. EP 0 881 858 A2 with a single filament arranged in around tube and in German published patent applications Nos. DE 44 38 871A1 and DE 44 19 285 A1 with several carbon filaments arranged next toeach other. The carbon materials used there consist of parallel carbonfibers, which are connected by resin. These structures are carbonizedand graphitized before installation in the radiator.

The radiator disclosed in EP 0 881 858 is not suitable for uniformtwo-dimensional radiation. DE 44 38 871 and DE 44 19 285 relate to theuse of comparable filaments, but with the goal of achievingtwo-dimensional (2D) radiation.

However, the carbon filaments disclosed in these documents cannot beassembled into arbitrary two-dimensional heating elements, because thematerial can have only an elongated and constant width arrangement. Thearrangements shown in DE 44 38 871 can realize this configuration, butneither uniform radiation intensities, nor such bent or round shapes, oreven 3D shaped structures, can be realized.

Even the arrangement shown in DE 44 38 871, FIG. 5a exhibits aconsiderable variation in temperature, and thus of the radiated outputper unit of length in the bands located at the edge, due to thedifferent lengths of the different fibers. Arrangements with a pluralityof narrow bands, like those in DE 44 19 285, require a plurality ofcomplicated and expensive contacts for the individual bands relative toeach other.

However, such carbon bands cannot be arranged in arbitrarytwo-dimensional patterns, because the bands only permit minimaldeviations from a parallel arrangement. Bands can be arbitrarily formedperpendicular to their two-dimensional configuration. However, sucharrangements lack the two-dimensional character of a radiating surface.

The present invention also relates to the use of CFC material forradiant heaters.

Japanese published patent application No. JP 7-161725 A1 describescutting out a heating pattern from planar material, wherein siliconcarbide (SiC) is used. The SiC heating element there is located in anopen housing made of quartz glass, on which a graphite disk (see FIG. 1,No. 8) is placed on the side used for the heat treatment. The graphitedisk is heated by the SiC heater and then secondarily warms thematerial. Such heating elements made of SiC or graphite are brittle andrigid, so that they are very sensitive to fracture. The heating elementis also electrically contacted rigidly by screws, so that heat expansionintroduces there an additional risk of fracture. To guarantee sufficientmechanical strength in such heating elements, these must be constructedvery large. Due to the low electrical resistance present there, veryhigh currents flow during operation at low voltages. This requirescomplicated power-grid supply circuits and the electrical supply linescan be guided into a vacuum-tight quartz body only with difficulty. Forthis reason, the quartz glass housing there also has an open shape.

European Patent No. EP 0 899 777 B1 describes a carbon heating devicewith a heating device member made of carbon fiber bundles extending in alongitudinal direction and interwoven with each other, such as a band orwire shape. These interwoven carbon fiber bundles are expressly not bygraphite expressly not converted into CFC by graphite. Thus, thesebundles remain very flexible, and the risk of brittle fracture isavoided. The described wire-shaped or band-shaped heating deviceelements have a high electrical resistance, so that the heating devicecan be designed to operate at common voltages. Due to the very lownumber of fibers in the band, however, even at maximum output only arather small current of a few amperes flows, so that overall theelectrical output of such a unit turns out to be rather small at 30kW/m^(2.)

The heating device element is laid in channels, which have been milledin a first quartz plate. Then the heating device is sealed by a secondquartz plate, which is laid on the first plate and connected to it. Theconnection is realized by placing a weight of 10 kg and a heatingprocess, in which the entire device is heated to 1450° C. for 3 hr. Theresulting connection of the two quartz plates is not a continuous weldand, after long-term operation, gaps can appear due to mechanicaland-thermal loads.

According to U.S. Pat. No. 6,584,279 B2, an IR radiator with anelectrical output of up to 28 kW/m² is obtained with braided carbonfibers.

In braking technology, carbon fiber-reinforced carbon (CFC) disks madeof CFC material or Si-impregnated CFC are used.

BRIEF SUMMARY OF THE INVENTION

The goal of the invention is to develop an IR radiator, which can beoperated at typical power-grid voltages, at the same time has highoutput and long service life and permits a large degree of flexibilityin possible configurations in terms of the required shapes of theprocess.

According to the invention, it was surprisingly discovered that with theuse of complex shape filaments for carbon radiators, which were cut fromCFC sheets, surface outputs of over 30 kW/m², in particular over 100kW/m², can be produced. It was further surprisingly discovered that whenthese filaments are placed in a housing, which comprises opaque quartzglass on the bottom side and on the top side clear quartz glass that issandblasted or frosted except at the surface, IR radiation is radiatedprimarily only from the top side. The hot quartz glass itself doesradiate in the range of long-range infrared above 5 μm and the radiatedoutput in this wavelength range is independent of the quartz materialused or the surface. However, only this secondary portion of theradiation appears at the bottom side of the device according to theinvention.

By selecting a suitable CFC material of high specific electricalresistance, as produced, for example, by using a thread that wasproduced from a plurality of short fiber sections and then wasinterwoven into a web, a suitable specific electrical resistance can beset. Such webs also remain flexible and tear-resistant afterimpregnation and conversion into CFC. Filaments of complex shapes cutfrom CFC sheets also remain flexible and tear-resistant.

Because the thickness of the material is low, preferably <about 1 mm andparticularly preferred <about 0.3 mm, an electrical resistance of thefilaments, which enables the operation at typical operating voltages(208 V, 230 V, 400 V, 480 V), is also achieved. Typical currentleadthroughs for IR radiators permit approximately 25 A, so thatconsiderable outputs per filament can be realized.

According to the invention, it was surprisingly discovered that in flatradiant heaters with patterns made of a CFC web, outputs of over 30kW/m², particularly over 100 kW, can be achieved, and radiators with anoutput of about 8-12 kW can be produced. The planar radiators canradiate on one side, if a planar carbon pattern is arranged between twosurfaces, of which one is opaque and the other is clear. The inventioncan also be realized with several CFC webs.

In this manner, heating technology is provided, which is of the higheststandard for super-clean applications, such as those required in thesemiconductor industry.

In preferred embodiments of the invention, planar quartz glass elements,or plates, of the housing are welded, adhered or soldered to each otherto form a housing. Preferably, at least one of these plates isreflective to IR or at least partially transparent to IR. The housingcan be manufactured from a high-purity material, for example quartzglass. The CFC heating filament can be arranged in the housing onholders, wherein the shape of the holders is preferably selected so thatthe contact surface is kept small, ideally limited to a line. Suitableholders comprise, for example, rods made of quartz glass, aluminumoxide, or other non-conductive material with a high melting point, andideally are formed as bodies with a sharp edge on which the filamentlies.

Preferably, the output of the radiant heater equals more than about 30kW/m², particularly about 50 to 250 kW/m², for radiant heaters with aservice life of about 5000 to 10,000 hours.

Another preferred embodiment consists in radiant heaters with an outputof over about 200 kW/m², particularly over about 250 kW/m², forshort-lived radiators.

The particularly preferred field of application is a long-lived radiantheater with an output of about 100 to 200 kW/m².

In the preferred shape of a surface radiator, two spatial dimensions aremore pronounced by a factor of at least about five, and preferably byabout one to two orders of magnitude, than the third dimension. Forexample, as shown in FIG. 6, the radiant heater housing may have spatialdimensions X, Y, and Z, which are orthogonal with respect to each other.The housing is preferably more pronounced in the X and Y spatialdimensions than in the Z spatial dimension at least by a factor of aboutfive, and more preferably by at about one to two orders of magnitude.Such spatial dimensions have proven effective to evacuate the housing orto fill it with inert gas.

The electrical contact of the filament is realized preferably by clipsmade of molybdenum, wherein additional layers made of suitable carbonmaterials between the filament and the clip provide an ideal electricaland mechanical contact.

Preferred CFC patterns are disk-shaped, meander-shaped, spiral-shaped,omega-shaped, a folded-in omega shape, or circular with a recess. TheCFC pattern can be cut particularly cleanly from a CFC sheet with thenecessary accuracy and by careful handling of the material with a laseror water jet.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown. In thedrawings:

FIG. 1 a is a plan view of a heating element 1;

FIG. 1 b is a perspective view of the heating element 1;

FIG. 2 a is a plan view of a base plate 2;

FIG. 2 b is a perspective view of the base plate 2;

FIG. 3 a is a plan view of a cover plate 3;

FIG. 3 b is a side view of the cover plate 3;

FIG. 4 is a perspective view of the base plate 2 with the mounted supplylines of the electrical contacts 26 and the mounted pump nozzles 27; and

FIG. 5 is an overall perspective view of the device from below.

FIG. 6 is a perspective view of the radiant heater housing having aheating element therein, with respect to three spatial dimensions.

DETAILED DESCRIPTION OF THE INVENTION

A heating element according to FIG. 1 a or 1 b is cut out from a sheetmade of CFC material.

The base plate 2 according to FIG. 2 a or 2 b is produced from opaquequartz glass, preferably a quartz glass having a diffuse reflection ofgreater than about 90% and more preferably greater than about 95%. Inits surface, there are contact pieces 22 for the heating band 1, spacers23, which are welded to the cover plate, and positioning pins 21 forfixing the heating band 1. An edge 24 for welding to the cover plate isprovided peripherally on the outside. Furthermore, two bore holes 25 areprovided for the electrical contacts.

FIGS. 3 a and 3 b show a cover plate 3 made of quartz glass withcounter-bored openings 31 for welding the cover plate to the spacers 23of the base plate 2.

In FIG. 4, the base plate 2 is equipped with mounted supply lines of theelectrical contacts 26 and the mounted pump nozzles 27.

In FIG. 5, the electrical supply lines 28 and socket 29 are alsoattached.

The radiant heater according to FIG. 5 has a CFC heating element 1(FIGS. 1 a and 1 b), which fills out the entire surface to be heated ina meander pattern. Underneath the ends of the filament 1, two tubes madeof quartz glass for receiving the electrical contacts 26 and the currentleadthroughs contact the base plate 2 (FIGS. 2 a/2 b) made of quartzglass (OM-100 according to Heraeus brochures from 2002). The front side3 is a clear quartz glass panel 3. The disks 2 and 3 are sealed to forma tight space, which is evacuated by the tubes for the current supplylines. In this configuration, the carbon band 1 can be heated toapproximately 1300° C. at an output of 200 kW/m².

In a simple configuration according to FIGS. 2 a and 2 b, the opaquedisk is formed as a base plate 2, on which spacers 23 are arranged. Thebase plate 2 is bounded by an inner and an outer ring 24. The CFCpattern 1 lies loosely on the contact pieces 22, and a clear quartzglass plate 3 forms a seal with the rings.

In FIG. 2, the current leadthroughs are located outside the circularradiation unit and require a deviation from the disk or ring shape forthe glass plates 2, 3 and rings. In this configuration, the carbon band1 can be heated to approximately 1300° C. at an output of 200 kW/m².

For ultra-high purity applications, the CFC pattern 1 is cut from a CFCsurface with a laser. The spacers 23 and also the rings and the quartzglass plates 2, 3 consist of ultra-high purity quartz glass, so that, inaddition to the metallic current supply lines and the molybdenumretaining clips connecting the web ends to the current leadthroughs,only high-purity quartz glass is used as the radiator housing andhigh-purity carbon is used as the radiation source 1.

PRODUCTION EXAMPLE

An opaque quartz glass plate 2 of sufficient thickness is cut into thenecessary shape for the bottom side 2, then the recesses are milled andground. In this way, the edge 24 and the spacers 23 remain at theiroriginal height and the contact pieces 22 for the filament stand at alower height. Finally, the openings, in which the tubes for the electriccontacting and the current leadthrough are placed, are bored. Edges aresmoothed or fire-polished, if necessary.

Then tubes made of quartz glass are set on the bore holes, in each ofwhich tubes a current leadthrough is arranged. Additionally, nozzles 27for establishing a vacuum and for introducing flushing gas are locatedat these tubes.

The cover plate 3 for the top side is cut and ground from pure quartzglass. In particular, openings 31 for later welding of the plate to thespacers 23 of the opaque plate 2 are formed.

The heating element 1 is cut from a CFC sheet material by a water jetand then coated with pyrocarbon in a reactor.

Current leadthroughs are produced in the shape of crimped sections. Amolybdenum pin is located at the inner end of the current leadthrough.The clamp for receiving the heating element 1 is attached to this pin.

The current leadthrough is welded to the tube of the currentleadthrough, so that the clamps for receiving the filament are alreadylocated in the later plane of the filament. Then, the band is laid onthe bottom side, and the band ends are connected in a clamped manner tothe current leadthrough by the molybdenum sheet retaining clip. Here,for mechanical protection and for improving the electrical contact,additional small graphite layers are deposited.

The cover plate 3 is placed and the resulting interior is flushed withargon, so that during the welding process, water vapor or oxygen cannotoxidize the carbon or the molybdenum.

Then, the two quartz elements 2, 3 are welded to each other. In thisway, the weld is connected by applying additional quartz glass along theedge and at the openings 31 in the cover plate, which lie opposite thespacers 23 for the cover plate. After completion of the weld, theopenings in the cover plate are completely filled and also the edgesbetween the top and bottom plate are filled so that there are no longerany gaps.

Then, the body is tempered under a vacuum or under a protective gas. Theprotective gas is fed directly into the body and flushes this bodyduring the entire tempering process.

After the tempering, the surface is ground, polished, lapped, orsandblasted and then cleaned by acid. After this process, the top sideis absolutely flat.

The interior of the radiator is either evacuated or filled with aprotective gas and the radiator is sharpened.

The electrical contacts are attached on the outside.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

We claim:
 1. An IR radiant heater comprising at least one planar carbon heating element (1) in a housing, the housing being at least partially transparent to IR radiation, wherein the at least one carbon heating element (1) is a carbon fiber-reinforced carbon web arranged in a plane and arranged between a first plate (2) and a second plate (3), at least one of the first plate (2) and second plate (3) being at least partially transparent to IR radiation.
 2. The IR radiant heater according to claim 1, wherein the first plate (2) is reflective for IR radiation.
 3. The IR radiant heater according to claim 2, wherein the IR reflective first plate (2) comprises opaque quartz glass.
 4. The IR radiant heater according to claim 3, wherein the opaque quartz glass has a diffuse reflection of greater than about 90%.
 5. The IR radiant heater according to claim 4, wherein the opaque quartz glass has a diffuse reflection of greater than about 95%.
 6. The IR radiant heater according to claim 3, wherein the IR reflective first plate (2) comprising opaque quartz glass is a base plate welded or adhered or soldered to a transparent cover second plate (3).
 7. The IR radiant heater according to claim 1, wherein the housing has a X spatial dimension, a Y spatial dimension, and a Z spatial dimension, and wherein the housing is more pronounced in the X and Y spatial dimensions than in the Z spatial dimension, at least by a factor of about five.
 8. The IR radiant heater according to claim 7, wherein the housing is more pronounced in the X and Y spatial dimensions than in the Z spatial dimension, at least by about one to two orders of magnitude.
 9. A method for producing an IR radiant heater having at least one planar carbon element (1) arranged in an at least partially IR radiation-transparent housing, comprising cutting the carbon heating element (1) from a planar carbon fiber-reinforced carbon material.
 10. A method for producing an IR radiant heater having at least one carbon fiber-reinforced planar carbon element (1), comprising arranging the carbon fiber-reinforced planar carbon element (1) between a clear surface (3) and an opaque surface (2). 